When it comes to the operation and optimization of modern HVAC systems, building owners and operators face two main challenges:
• Inadequate training. Many building operators find themselves responsible for technologies more advanced than their technical skills and expertise. Often, it is assumed that whatever does not work, was not installed properly, or was not tested fully will be identified and corrected by the appropriate subcontractor during the warranty period. However, even if a non-performing system is corrected, the cost (waste) in terms of dollars, kilowatt-hours, and therms will have been substantial—not only for the building owner, but for the subcontractor.
• Controls complexity. In most cases, relatively simple pneumatic controls have given way to direct digital controls (DDC) and a host of new terms and technologies, such as PID, BACnet, LON, Ethernet, ARCnet, TCP/IP, WAN, LAN, WAP, WML, XML, CORBA, SOAP, and Enterprise. Additionally, rather than the three or four suppliers that dominated the pneumatic-controls industry 30 years ago, there are dozens of DDC manufacturers.
Building commissioning, recommissioning, and retrocommissioning are valuable services aimed at overcoming these and other challenges affecting the operation and optimization of HVAC systems. However, many building owners assume that once one of these services is performed, nothing more needs to be done. System degradation and whether their building continues to operate at peak efficiency is not on their radar, so to speak. They fail to realize that filter and belt replacement, oil changes, bearing inspections, and the like only scratch the surface of what should be done on a continuous basis to keep a building operating at optimum levels.
This article discusses Continuous Commissioning, a process that can provide tremendous benefits for commercial buildings.
Continuous Commissioning Defined
Continuous Commissioning—as defined by the Energy Systems Laboratory (ESL), a division of the Texas Engineering Experiment Station, which trademarked the term, and a member of the Texas A&M University System—is an ongoing process to resolve operating problems, improve comfort, and optimize energy use. Typically, it is implemented in two phases and consists of the following seven steps:
1) Visit the site to identify and quantify potential measures and savings.
2) Develop performance baselines for energy and comfort.
3) Examine the building in detail—to the air-handling-unit (AHU) and/or terminal-box level—to identify operating and comfort problems, component failures or degradation, and causes of system inefficiency.
4) Implement Continuous Commissioning measures.
5) Identify changes in operating procedures for the building staff, and document energy savings and comfort improvements in accordance with the International Performance Measurement and Verification Protocol (IPMVP).
6) Train the building staff.
7) Track/verify energy and comfort performance for at least one year in accordance with the IPMVP.
To fully grasp what Continuous Commissioning is, one must understand how it differs from other types of commissioning. Most would agree that commissioning, recommissioning, and retrocommissioning verify that a building's mechanical and electrical systems are operating in accordance with original plans and specifications; the primary difference is the point in time at which each is conducted and whether or not commissioning had been performed previously. While retrocommissioning can offer operational improvements and energy savings above and beyond original plans and specifications, Continuous Commissioning goes a step further, involving the continuous collection and analysis of energy data via an existing building-automation system (BAS) and/or stand-alone metering equipment.
Nearly every building today is designed with energy efficiency in mind. Variable-frequency drives (VFDs), chillers with low kilowatt-per-ton requirements, and highly sophisticated BAS are designed into most major commercial office buildings, hospitals, and schools. Simply designing, installing, and verifying (commissioning) these technologies, however, is not enough, if energy use is to be optimized over the long term.
In a study of 60 new buildings conducted by Lawrence Berkeley National Laboratory, 50 percent of the buildings suffered controls problems, 40 percent suffered HVAC problems, 15 percent had missing equipment, and 25 percent had energy-management systems, economizers, and VFDs that did not function properly.1 Remember, this was a study of new buildings. Existing buildings almost certainly would have fared far worse simply because of natural HVAC-system degradation and changing building conditions.
Continuous Commissioning not only preserves long-term savings potential, it improves system reliability and comfort as building conditions change. When Continuous Commissioning is implemented properly, reasonable expectations for payback and savings are less than three years (Table 1) and 20 to 30 percent, respectively.
|TABLE 1. Average payback with Continuous Commissioning.2|
In his presidential address,3 2008-2009 American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) President William A. Harrison cites a study conducted by the ESL, saying: "Energy use in buildings could be reduced by 10 to 40 percent by improving operational strategies in buildings. This reduction in energy was not so much the result of changes in hardware and systems as it was the result of improvements in software and expert knowledge."
HVAC systems should operate at optimum levels long after original commissioning. Too often, buildings that were formally and properly commissioned wind up with Energy Use Indexes (EUIs) three and four times the industry standard within a few years.
With the sophistication of today's BAS, deterioration often goes unnoticed because controls have "learned," or "adapted" to, the changing conditions of a building and/or HVAC equipment. Still, operating costs can increase by as much as 50 cents per square foot per year.
Take, for instance, an AHU with the ability to "remember" how long it took the day before to produce a desired temperature in a space. If the mechanical status of the AHU has degraded, or sensors have fallen out of calibration, the AHU's DDC sequence might tell the AHU that to achieve the same results it did by starting at 6 a.m., it must start at 5:30 a.m. At this point, there are two choices: abandon the "learning" capability of the software, or clean the coils, change the filters, and calibrate the sensors. The cleaning of coils and changing of filters are routine maintenance tasks, while the calibration of sensors and verification that operating routines are optimized are best addressed with Continuous Commissioning.
Continuous Commissioning has been utilized extensively on the campus of Texas A&M over the last 15 years. Total savings of $60 million have been realized with investments of approximately $10 million in Continuous Commissioning and $8 million in capital improvements. The university's EUI has been in steady decline since 1998 (Figure 1).
|FIGURE 1. Energy use per gross square foot on the Texas A&M campus.|
In a Utah state office building already considered energy-efficient, the energy-cost index was reduced from $1.07 per square foot per year to 77 cents per square foot per year for a total savings of $116,000 and a payback of 1.2 years as a result of Continuous Commissioning in 2001.
Over the last 10 years, Continuous Commissioning has been implemented in more than 300 buildings across the United States by the ESL and its authorized licensees. With the complexity of today's HVAC systems and controls, rising energy costs, increased focus on energy supply and source, and a "green" consciousness that has begun to permeate our decision making both at work and at home, Continuous Commissioning is a unique, easy-to-implement, and cost-effective way to reduce energy consumption in commercial buildings.
1) HPCBS. (n.d.). Integrated commissioning and diagnostics. Retrieved from http://buildings.lbl.gov/hpcbs/Element_5/02_E5.html
2) Bynum, J. (2008, October). The cost-effectiveness of Continuous Commissioning over the past ten years. Paper presented at 8th International Conference for Enhanced Building Operations, Berlin.
3) Harrison, W.A. (2008). Maintain to sustain—delivering ASHRAE's sustainability promise. Retrieved from http://www.ashrae.org/aboutus/page/1870
The manager of Continuous Commissioning for SSRCx LLC (www.ssrcx.com), a commissioning provider specializing in hospitals, research laboratories, sports facilities, and other complex buildings, Steve Harrell has 25 years of sales, implementation, project-management, and executive-management experience related to building-automation systems. He has a bachelor's degree in industrial management and management science from The University of Tennessee, Knoxville.